Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1999-11-02
2001-12-04
Chapman, John E. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C702S147000
Reexamination Certificate
active
06324909
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to signal processing techniques for rotation sensor systems used in navigation and other applications. More particularly this invention relates to signal processing techniques in rotation sensor systems that include Coriolis acceleration sensors for measuring rotations.
Angular rate can be measured with a captured linear accelerometer by mounting it on a vibrating frame and measuring the Coriolis accelerations generated by the angular rate of the frame relative to inertial space. Generally to attain precise angular rate measurement, the frequency response of such accelerometers must be well defined at the vibration frequency of the dithered frame. The scale factor is directly related to the accelerometer closed loop gain. Large errors can be generated from the vibration drive motion coupling into the accelerometer if the measure of this motion is not rejected by accurate control of the phase of the reference in the demodulation of the Coriolis signal.
One technique for eliminating the large errors due to uncertainties in the gain and phase of the accelerometer output is to use precision AC torque feedback to exactly cancel the Coriolis forces developed by the rate, thereby maintaining an absolute null of the proof mass at the dither frequency.
In some feedback control systems the parameter being measured varies the amplitude of a sinusoidal carrier signal. In such systems the frequency of the carrier signal is normally much higher than the desired bandwidth for the parameter being measured. Such amplitude modulated signals may be generated from sensors that measure pressure, acceleration, velocity, angular rate, and the like. For some of these sensors, precise measurement of the parameter is determined by measuring the feedback signal required to maintain a balance in a closed loop configuration.
An application where precise measurement of a modulated signal is important is a vibrating angular rate sensor system that measures the Coriolis acceleration generated by an angular rate input. A constant rate input to such a sensor causes an output signal that is amplitude modulated at the frequency of the driven oscillation of the device. The generated Coriolis acceleration is proportional to the input rate and is 90° out of phase with the driven vibration amplitude. Therefore, the maximum acceleration occurs when the maximum vibration velocity occurs, which is 90° out of phase relative to the maximum amplitude of vibration. In most cases the rate sensor is a built-in acceleration detector or a small accelerometer mounted on the vibrating member. The proof mass of the detector responds to the Coriolis acceleration generated by the rate.
If the acceleration sensor is operated in an open loop configuration, then its frequency response must generally be much higher than the driving frequency if the gain and phase of the output signal are to be well-defined. The absolute value of gain is important for scale factor, and the phase of the signal relative to the driven reference oscillation is important in order to reject any “quadrature” signal, which is a major source of error in rate measurement. This same gain and phase difficulty will also occur in closed-loop acceleration sensing if typical capture loop techniques are used.
SUMMARY OF THE INVENTION
This invention provides an acceleration sensor system having a proof mass that is made free of feedback in the accelerometer servo loop at the driven frequency by totally notching out all feedback torque at this frequency. The proof mass relative motion is then a direct measure of the rate because there is no feedback torque to alter the proof mass response to the acceleration. In such a case the proof mass is essentially responding in an open loop mode where the amplitude and phase of the motion are well defined relative to the dither drive. The acceleration sensor system according to the invention is particularly useful in sensing Coriolis accelerations.
The present invention provides a technique for overcoming the difficulties of previous feedback modulation techniques for amplitude modulated servo systems. The feedback modulation system according to the invention captures the Coriolis-sensor such that the phase and gain of the signal generated from the sensor are of no concern in maintaining good scale factor. The apparatus according to the invention includes a feedback loop connected between the output of the servo compensator and the summer. The feedback loop includes a torquing remodulator. The sensor, the demodulator, the servo compensator and the feedback loop with the torquing remodulator cooperate to produce a measured output that is independent of the gain and phase of the sensing dynamics, the demodulator and the servo compensation.
The apparatus according to the present invention for processing signals output from a Coriolis force sensor to measure angular rate comprises a demodulator connected to the sensor to receive signals indicative of the angular rate output therefrom and a servo compensator connected to receive signals output from the demodulator. The servo compensator produces a rate output signal {dot over ({circumflex over (&phgr;)})}(s) that is indicative of the measured value of the angular rate. A feedback loop that includes a torquing remodulator is connected between the servo compensator and the sensor. The torquing remodulator applies a remodulated angular rate signal to the sensor such that the demodulator, the servo compensator and the feedback loop cooperate to produce a measured output that is independent of the gain and phase of the sensor, the demodulator and the servo compensator.
The apparatus according to the present invention for processing signals output from a sensor to measure angular rate may also be comprised of dither apparatus for driving the sensor with an oscillatory angular velocity signal of a frequency &ohgr;
D
and a demodulator connected to the sensor to demodulate signals output therefrom with a signal proportional to cos (
107
D
t) to produce a rate output signal {dot over ({circumflex over (&phgr;)})}(s). A feedback loop is connected between the sensor output and the dither apparatus. The feedback loop includes a servo compensator connected to receive signals output from the sensor and a notch filter connected between the servo compensator and the dither apparatus. The notch filter is arranged to reject signals of the dither frequency &ohgr;
D
to make the feedback loop carry no signal that would produce feedback torque in the sensor at the dither frequency. Therefore, relative motion of the sensor is a direct measure of the angular rate.
The invention may alternatively comprise a high pass filter connected to the sensor pickoff and an in-phase signal processing channel connected to the high pass filter. The in-phase signal processing channel preferably includes a cosine demodulator arranged to receive signals output from the high pass filter and a first servo compensation circuit connected to the cosine demodulator to produce a rate measurement signal. A cosine remodulator is connected to the first servo compensation circuit. A quadrature-phase signal processing channel is connected to the high pass filter. The quadrature-phase signal processing channel includes a sine demodulator arranged to receive signals output from the high pass filter and a second servo compensation circuit connected to the sine demodulator. A sine remodulator is connected to the servo compensation circuit. A first summer is connected to the cosine remodulator and to the sine remodulator. An acceleration feedback loop is connected between the sensor pickoff and the second summer. The acceleration feedback loop includes a notch filter arranged to reject signals of the dither frequency &ohgr;
D
to make the feedback loop carry no signal that would produce feedback torque in the sensor at the dither frequency, such that relative motion of the sensor is a direct measure of the angular rate, and such that the notch filter produces a signal indicative of t
Flamm Juergen K. P.
Lee Charles A.
Tazartes Daniel A.
Wyse Stanley F.
Chapman John E.
Litton Systems Inc.
Lynn & Lynn
LandOfFree
Signal processing system for inertial sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Signal processing system for inertial sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Signal processing system for inertial sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2585924